PPS Electrical Safety Guidance for the Electrical Contractor: Cable Extensions

1: Introduction

It is normally the case that the 10m cable attached to the pump is long enough to connect into the isolator or fused connection unit, provided by the Electrical Contractor, without any additional connection/terminations being necessary. However, occasionally the location of the pump/isolation requires the supply cable to be extended.

Accordingly, the recommendations provided in this document are for the installation of conductors/cables when there is a need to extend the supply cable.

2: Assessment of general characteristics

It is the responsibility of the electrical contractor undertaking the fixed wiring to the isolator or fused connection unit to undertake an assessment of the existing condition of the electrical installation to ensure, amongst other things, that those parts of the installation related to the new circuit, meets the requirements of BS 7671, the Wiring Regulations, in particular with regard to earthing and bonding. The electrical contractor will also need to determine the maximum demand of the existing installation and take account of the additional load proposed. Due regard must also be paid to continuity of supply and resilience of the new radial circuit

3.1 Within Chamber

Should the pump installation require a longer connecting cable, then these terminations must be within the appropriate enclosure that meets IP Code IP67 as a minimum. The Electrical Contractor must ensure that all connections are electrically and mechanically sound and that the enclosure is appropriate for the external conditions likely to occur.

3.2 Outside Chamber

Should the pump installation require a longer connecting cable, then these terminations must be within the appropriate enclosure that meets the appropriate IP Code to meet the environmental conditions likely to be encountered. The Electrical Contractor must ensure that all connections are electrically and mechanically sound and that the enclosure is appropriate for the external conditions likely to occur.

4: Cable selection

The connecting cable is to be at least the same size and type as the original cable that the manufacturer provided. Additional connecting cable exceeding 10m in length should not be installed without specific design of cable size and voltage drop calculations being undertaken by the Electrical Contractor or competent Design Engineer.

Typical cable types included:

• HO7RNF
• Steel Wired Armoured (SWA) thermoplastic
• Steel Wired Armoured (SWA) thermosetting

It should be noted that it is likely that only thermosetting cables would be acceptable in commercial/industrial installation, whilst within domestic premises, thermoplastic is likely to be acceptable. The Electrical Contractor is to consider all environmental conditions to which the cable may be exposed, such as rodent attack.

4.1: Current carrying capacity and volt drop

The Electrical Contractor should establish the starting and load (running) current of the pump to be installed. PPS will provide data relating to the pump characteristics. The Electrical Contractor should then select the appropriate cable for current carrying capacity. This current carrying capacity being dependent upon cable size, installation method and volt drop. Volt drop of the extended conductors shall not exceed 2%

4.2: Shock Protection

It is acknowledged that the provision of the RCBO at the origin of the installation is likely to provide both fault protection and additional protection. However, it is preferred that the electrical contractor ensures that the total measured impedance (Zs) of the radial circuit, including the cable extension, does not exceed the values provided in table 41.3 of BS 7671. The Wiring Regulations.

4.2: Thermal Constraints

To ensure that the cable and its conductor will not suffer damage during any earth fault conditions, the earthing conductor within the cables shall be sized accordingly.

If cables incorporating a reduced Circuit Protective Conductor (CPC) are selected, such as twin with earth, the overall length of the circuit, including the extension, shall not exceed the maximum lengths recommended in the IET On-Site-Guide. If SWA cables are selected, an additional core of the same CSA as the live conductors shall be used. That is 3-core (single-phase) or 5-core (3ph).

5: Requirements of BS:7671. The IET Wiring Regulations

The recommendations provided should not be considered to include all the recommendations provided within the IET Wiring Regulations (BS7671). The Electrical Contractor should ensure that all relevant parts of those Regulations have been considered during the design, installation and verification of the electrical installation.